If given very early in the course of an acute myocardial infarction (AMI) to proper candidates, thrombolytic therapy (TT) may reduce mortality by nearly 50%. Achieving TT's potential enormous impact on the most common cause of death in this country depends on developing ways to rapidly deliver TT to appropriate AMI victims. If given too late, or insufficiently selectively, TT may cause serious complications and incur substantial costs, while yielding little benefit. The TPI is intended for emergency department (ED) and emergency medical service (EMS) use to optimize TT outcomes by: 1) identifying those patients likely to benefit from TT, and 2) facilitating the earliest possible TT administration. Like our earlier predictive instruments for ED triage of patients with suspected AMI, the TPI is intended to assist real-time clinical decision- making. Based on multivariate regression models derived from our large database including major TT trials, the TPI will predict: 1) acute (30- day) mortality; 2)1-year mortality; and complications of TT, including 3) hemorrhagic stroke, 4) major bleeding, and 5) cardiac arrest. The TPI will provide clinicians 0-100% probability predictions for each outcome for if TT is used, and for if TT is not used. A computerized TPI electrocardiograph will print these predictions on the top of the electrocardiogram for ED and mobile EMS use. The clinical trial will allow accomplishment of 2 goals: 1) to demonstrate the clinical impact of the use of the TPI, and 2) to test the accuracy of the TPI's predictions. The clinical trial's 12-month patient inclusion period will employ alternating 1-month intervention/control periods. Study outcomes for the analyses of the TPI's clinical impact will include appropriateness of TT use (sensitivity and specificity) and speediness of TT use. For the testing of the TPI's predictions, the predicted outcomes listed above, including 1-year mortality, will be checked for accuracy, discrimination, and calibration. Completion of the TPI Clinical Trial should show the potential impact of the use of multiple clinical data sources for effectiveness research and of a new type of predictive instrument to promote effectiveness of an important therapy in the actual clinical setting, and hopefully will lead to the saving of many lives.